Israeli soldiers are briefed at a staging area on the Israel-Gaza border,just outside the northern Gaza Stip, Wednesday Jan. 21, 2009. Israel withdrew the last of its troops from the Gaza Strip before dawn on Wednesday, the military said, as the government pursued diplomatic efforts to stanch the flow of arms into the Hamas-ruled territory. (AP Photo/Tsafrir Abayov)

As Israel's last troops left the Gaza Strip Wednesday, Hamas officials conceded that they are executing Palestinians suspected of collaborating with Israel during the three-week invasion.

In the West Bank, Fatah officials said at least 19 of its members have been executed and many more brutally tortured. Gaza residents say Hamas is using schools and other public buildings in Gaza City, and the towns of Khan Yunis and Rafah as detention centers to interrogate members of Fatah, their political rivals. They said three men have been blinded during questioning and more than 60 have been shot in the legs as punishment.

"They are committing human rights violations in a very brutal manner," Mahmoud Habbash, Palestinian Authority minister of social welfare said in Ramallah. "Not only did Israel perpetrate war crimes, but Hamas also has been targeting innocent Palestinians."

'Kisses to Israeli warplanes'

A leaflet distributed by the Fatah military wing, the Al-Aqsa Martyrs Brigades, pleaded with Hamas to "respect the blood of the Palestinian martyrs" and urged them to stop pursuing Fatah members in Gaza. The leaflet said Hamas has arrested hundreds of Fatah members since the cease-fire and has threatened to shoot anyone who refuses to surrender.

While Fatah leaders in the West Bank also accused Hamas of stealing U.N. aid convoys, Hamas officials denounced Palestinian Authority President Mahmoud Abbas and his Fatah movement for collaborating with Israel and said they no longer recognized his authority since his term officially ended on Jan. 9.

In Damascus, Moussa Abu Marzook, the Hamas deputy political leader, told reporters that senior Fatah officials had "distributed candy celebrating the Gaza offensive, sent kisses to Israeli warplanes" and "guided these planes to their targets." Admitting that suspected collaborators were being executed in Gaza, Abu Marzook said "many people from the former Palestinian Authority viewed the Israeli offensive as an opportunity to rise to power again" in Gaza.

Bitter rivals

Hamas and Fatah have been bitter rivals since June 2007, when Hamas ousted Fatah from Gaza after launching a bloody coup against the Abbas government. About 400 Fatah supporters were killed and many others badly maimed.

Since the 23-day Israeli assault on Gaza ended in a cease-fire Sunday, Hamas has repeatedly accused Abbas of backing Israel and has branded him a traitor and collaborator. On the first day of the invasion on Dec. 27, Hamas leader Khaled Mashaal called on Palestinians in the West Bank to overthrow the Abbas government in a "quiet intifada." More recently, Mohammed Al-Ghoul, Hamas justice minister, said Abbas should be put on trial for conspiring against the Palestinian people "in full coordination with the Israeli occupation."

Ihab Ghissin, a spokesman for the Hamas Ministry of Interior in Gaza, confirmed the arrest of Fatah activists. "We have managed to capture a number of collaborators who are now being questioned for their role in aiding the Zionist aggression," he told reporters in Gaza City.

Fatah officials have dismissed the accusations of spying for Israel, pointing out that Abbas has described Israel's three-week offensive as "barbaric and criminal." On Tuesday, Abbas backed an Arab League statement that accused Israel of war crimes. On Wednesday, a Fatah flyer calling West Bank residents to attend mass rallies today to condemn the invasion said "Israeli aggression did not distinguish between Palestinian factions."

David Makovsky, director of the Washington Institute's Project on the Middle East Peace Process, says Hamas has been hurling spy accusations at Fatah since the takeover of Gaza.

"It's clearly more palatable to Hamas to accuse Fatah of collaborating with Israel than to openly admit their desire for raw power over Gaza," said Makovsky.

Hamas proof

But Hamas legislator Salah Bardaweel said he has proof that Fatah helped Israel assassinate security chief Said Siam, commander of the 15,000-strong Hamas Executive Force militia. Siam was killed along with his brother and another senior security official in an air strike last week. Bardaweel said Fatah informants reported directly to Abbas officials in the West Bank.

"We had arrested a number of them prior to the Israeli assault, and we found them with plans showing homes of Hamas' leaders, and places where Hamas stores its weapons. They have admitted their guilt and told us names of their masters, who would, in turn, inform the Israeli intelligence ... to facilitate the Israeli mission," said Bardaweel.

Relatives of Abed al-Gharabli, a former Fatah security officer who spent 12 years in an Israeli prison, said he was kidnapped by a group of Hamas militiamen who shot him in both legs after severely torturing him.

Ziad Abu Hayeh, a Al-Aqsa Martyrs Brigade commander, is reported to have been blinded after being abducted from his home in Khan Yunis by Hamas gunmen.

In other cases, Fatah supporters were simply shot in the legs - a favored Hamas tactic during the 2007 coup that drove Fatah out of Gaza.

The crackdown suggests it will not be easy to bring Hamas and Fatah together in a national unity government that many observers believe is the only way to lift international sanctions against Gaza and ensure the speedy flow of goods to a population in desperate need of aid. The European Union has said it will not give reconstruction funds to Hamas, only to the Abbas government.